Fix sqlite3 gsub in Refinery::CmsGenerator

[parndt]

I noticed when running rails new -m https://www.refinerycms.com/t/edge
that it was mangling the Gemfile when the sqlite3 line looked like:

  gem 'sqlite3', '~> 1.4'

Instead of the expected:

  gem 'sqlite3'

Our gsub_file instruction now captures the entire line and inserts it
inside the group :development, :test do block.